stop/start services

I have just installed Postfix this morning as I was having problems with Sendmail. I begun
to configure the main.cf file but now PF will not start. I have made minimal changes and
have gone back and undone them all.

Is there an error log that I can look at to get some help?
Also, I have a couple of domain names that are not in use. Can I simply add the domain
name to the main.cf file and immediately start to send and receive mail over the net? My
ISP have changed mail servers and I have not had main for two whole days, either gets
bounced or just disappears into the Ether so decided to build my own server.

But what I need to know is that how can I get all mail sent via the net to
user@domain.co.uk to end up in my newly created mailboxes? Can I do this for myself or do
I have to register with some registered body?

Given that I own the domain name that my ISP services mail for, how can I wrestle control
of it from them? Apologies for all the questions, just answer when you can.

with thanks. JM